Co-channel interference receiver

Abstract

A digital receiver automatically detects and non-coherently demodulates a multiplicity of interfering digitally modulated signals transmitted simultaneously at approximately the same carrier frequency. The receiver includes one or more antenna inputs (e.g., polarization and / or space diverse), a parameter estimator module, and a multiuser detector for estimating the data transmitted by each interfering signals and adapted to operate with at least one of a MUD algorithm with partially quantized prior information and a MUD algorithm based on prewhitened data.

Description

RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Application No. 60 / 398,451, filed Jul. 24, 2002. This application is a continuation-in-part of U.S. application Ser. No. 10 / 228,787 filed Aug. 26, 2002, which claims priority to U.S. Provisional Application No. 60 / 372,956, filed Apr. 16, 2002. This application is also a continuation-in-part of U.S. application Ser. No. 10 / 105,918, filed Mar. 25, 2002. This application is related to U.S. application Ser. No. 10 / 423,695, filed Apr. 25, 2003, This application is related to U.S. application Ser. No. 10 / 423,655, filed Apr. 25, 2003. Each of these applications is herein incorporated in its entirety by reference.STATEMENT OF GOVERNMENT INTEREST[0002]The present invention was made with United States Government support under a United States Government Contract. The United States Government has certain rights in this invention.FIELD OF THE INVENTION[0003]The invention relates to wireless communications, and more...

AI Technical Summary

Benefits of technology

[0015]The analog front end may further include one or more antennas each configured to receive a corresponding composite waveform signal from the plurality of transmitters. In one such embodiment, the one or more antennas is a singly polarized antenna. Alternatively, the one or more antennas is a dual polarized antenna adapted with two polarization ports, thereby providing polarization diversity. Alternatively, the one or more antennas include two or more dual polarized antennas, each adapted with two polarization ports, thereby providing space and polarization diversity.

[0016]In an embodiment where the multiuser detector module is configured to operate with the low complexity linear MMSE algorithm with partially quantized prior information, the multiuser detector module includes a turbo MUD module, a combiner module, an error correction module, and a thresholding module. The turbo MUD module is adapted to provide estimates of individual bits for each of the K co-channel interfering signals. The estimates are iteratively applied in a feedback loop, which includes the error correction module, until an error rate associated with the bits drops below a predetermined figure. The combiner module is operatively coupled to the turbo MUD, and is adapted to combine recomputed bit estimates output by the turbo MUD with quantized bit values on a next iteration. The thresholding module is operatively coupled to the output of the error correction module, and is adapted to assign a quantized value for each bit estimate above a predetermined threshold, and to pass through those quantized bit values to the combiner module, thereby enabling partially quantized prior information. In one such embodiment, the error correction module on each subsequent iteration processes a combination of recomputed bit estimates output by the turbo MUD and quantized bit values output by the thresholding module, and provides its output back to the turbo MUD through the thresholding module, thereby reducing the number of uncertain bit estimates with every iteration.

[0017]In an embodiment where the multiuser detector module is configured to operate with the low complexity M-algorithm based on prewhitened data, the multiuser detector module includes a matched filter, a whitener designer module, an asynchronous whitener module, and a symbol hypothesis testing module. The matched filter is adapted to prewhiten complex signals received by the receiver, thereby partially decoupling users from multiple access interference. The whitener designer module is operatively coupled to the parameter estimator, and is adapted to develop a model of each received complex signal based on parameter estimates from the parameter estimator, and to compute an asynchronous whitener module that whitens filtered data output by the matched filter. The symbol hypothesis testing module is operatively coupled to the whitener designer module, and configured to receive whitened data output by the asynchronous whitener module. The symbol hypothesis testing module is adapted to conduct symbol hypothesis testing based on sequential evaluation of metric characterizing likelihood of hypotheses. In one such embodiment, the whitener designer module employs a square-root factorization. For example, the whitener designer module utilizes a correlation matrix provided by the parameter estimation module to compute a diagonally loaded Cholesky Factorization, which is used for whitening in the whitening module, and is also used in hypothesis testing in the symbol hypothesis testing module. Alternatively, the whitener designer module employs a QR factorization using Householder transformations. In addition, the whitener designer module can employ Hyperbolic Householder transformations to efficiently update the asynchronous whitener module when only received energies and / or phases change between symbol periods.

Problems solved by technology

Such schemes are inefficient in that given sufficient signal to noise ratio or coding redundancy, more communicators could use the allocated bandwidth if provided with a means for detecting the excess signal margin, as well as a means for demodulating signals in the presence of interference.

In short, despite the advancements in wireless transmission and reception, conventional systems do not properly account for the real world wireless communication signals that suffer from signal degradation such as interference and multipath problems.

Each of these transmissions are associated with real-time problems of multipath and co-channel interference that manifest in the received signals.

Co-channel interference refers to signals received from other users.

However, for multiuser detectors that examine a larger capacity of signal, the computations are complex and time-consuming, thus making real-time operation impractical.

However, performance of such multiuser detection algorithms degrades as the parameter M (pruning factor) is decreased, but M governs the number of computations required.

As a result, conventional pruning methods are still associated with increased complexity, particularly when the number of interfering signals is moderate to large.

Images